EP0108421B1 - NMR-Diagnosevorrichtung - Google Patents

NMR-Diagnosevorrichtung Download PDF

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Publication number
EP0108421B1
EP0108421B1 EP83111154A EP83111154A EP0108421B1 EP 0108421 B1 EP0108421 B1 EP 0108421B1 EP 83111154 A EP83111154 A EP 83111154A EP 83111154 A EP83111154 A EP 83111154A EP 0108421 B1 EP0108421 B1 EP 0108421B1
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EP
European Patent Office
Prior art keywords
magnetic field
coil
slice
gradient magnetic
axis
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Expired
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EP83111154A
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English (en)
French (fr)
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EP0108421A3 (en
EP0108421A2 (de
Inventor
Hiroshi Sugimoto
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Toshiba Corp
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Toshiba Corp
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Publication of EP0108421A3 publication Critical patent/EP0108421A3/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
    • G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
    • G01R33/4835—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices of multiple slices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils

Definitions

  • the present invention relates to a nuclear magnetic resonance diagnostic apparatus (to be referred to as an "NMR diagnostic apparatus" hereinafter) which utilizes the magnetic resonance phenomenon so as to noninvasively measure information as to the density and relaxation time of a specific atomic nucleus or proton within a selected sectional slice plane of an object to be examined, e.g., a patient, for which tomographic image is taken, and to display information for medical diagnosis in the form of tomographic images.
  • NMR diagnostic apparatus nuclear magnetic resonance diagnostic apparatus
  • a tomographic image plane (i.e., selected sectional slice plane) in a patient to be examined is limited to a plane which intersects a central point defined by gradient magnetic coils at which the strength of the gradient magnetic field is zero. For this reason, in order to obtain a plurality of adjacent sagittal images, the patient must be mechanically moved to the central point for each imaging.
  • a long time is generally required to collect data for obtaining one specific tomographic image by rotating the gradient direction of a gradient magnetic field at 360° in a plane perpendicular to the longitudinal axis of the patient with respect to the selected sectional slice plane to which a tomographic image is taken. Accordingly when more than one tomographic image is to be obtained, a still longer data collection time is required, resulting in a heavier imposition on the patient and disturbance in fast diagnosis.
  • Prior art document EP-A-0 055 058 discloses a nuclear magnetic resonance imaging apparatus which includes three gradient coils together with a coil for generating a steady field and a coil for providing RF fields.
  • a volume scanning of a region of a body to be examined is achieved by scanning in a first plannar slice of the region and scanning in at least one further planar slice of the region in the relaxation time for the scan of the first slice.
  • prior art document EP-A-0 105 485 having the priority date of 30.09.82 and published on 18.04.84 which is state of the art according to Article 54(3) EPC describes an apparatus for examining an object by NMR wherein the S/N ratio of an oscillator for generating a selective exciting pulse is improved to perform a highly precise diagnosis.
  • This apparatus uses first coil means, probe head coil means and second coil means for applying a first gradient field, RF pulses and a second gradient field to a slice of an object under examination, and enables zero intensity point shifting.
  • the present invention provides an apparatus for examining an object by nuclear magnetic resonance, said apparatus comprising magnet means for applying to the object a static magnetic field along a longitudinal axis thereof, first coil means which is arranged along the longitudinal axis and selectively energized so as to apply to the object a first gradient magnetic field that in conjunction with the static magnetic field gives a predetermined magnetic field in a slice of the object, and also to apply to the slice of the object a second gradient magnetic field for defining a projection angle of nuclear magnetic resonance signals; probe head coil means for applying RF pulses to the slice of the object so as to excite a nucleus therein to which is being applied the predetermined magnetic field super-imposed by the static magnetic field and the first gradient magnetic field, and for detecting the nuclear magnetic resonance signals derived from the slice of the object; and reconstruction means which receives the nuclear magnetic resonance signals obtained from the slice of the object through the probe head coil means with respect to a plurality of the projection angles of said first gradient magnetic field, and reconstructs a plurality of computerized tomography images for the
  • Fig. 1 shows the configuration of a nuclear magnetic resonance diagnostic apparatus 100 (referred to an an "NMR diagnostic apparatus” hereinafter) according to an embodiment of the present invention.
  • an oscillator 11 generates a selective exciting RF pulse H i .
  • Air magnetic field coils 12 extend perpendicularto a longitudinal axis Z of a patient P.
  • a probe head coil 14, three sets of gradient magnetic field coils 19, and three sets of gradient magnetic field shifting coils 20 are assembled within the coils 12, as shown in Fig. 2.
  • the air magneticfield coils 12 apply a static magnetic field H o to the patient P uniformly along the Z axis.
  • the RF pulse H 1 is applied to the selected sectional slice plane of the patient P through the probe head coil 14 in a direction of the Y axis which is perpendicular to the Z axis to cause a predetermined NMR phenomenon, thereby detecting from the patient P the NMR signals, e.g., echo pulse signals or free induction decay signals (FID signals).
  • NMR signals e.g., echo pulse signals or free induction decay signals (FID signals).
  • a stabilizer 13 is connected to the air magnetic field coils 12 for supplying stabilized power to the coils 12.
  • a power supply source 21 for supplying power to generate gradient magnetic fields G x , Gy, and G z in the X, Y and Z directions, respectively, is connected to the gradient magnetic field coils 19.
  • a power supply source 22 for supplying powerto the three sets of gradient magnetic field shifting coils 20 is connected thereto for spatially moving XY, YZ and ZX planes at which the gradient magneticfield is zero.
  • a duplexer 15 is connected to the output terminal of the oscillator 11. The duplexer 15 applies the RF pulse H, from the oscillator 11 on the patient through the probe head coil 14. Then, the duplexer 15 receives NMR signals produced by the specific atomic nucleus in the patient P. In this manner, the duplexer 15 serves as an RF switch and a tuned circuit.
  • An amplifier 16 amplifies an NMR signal received by the duplexer 15 from the probe head coil 14.
  • a digital arithmetic logic unit 17 performs various functions: A/D conversion of the amplified NMR signal, data processing involving calculation of a Fourier transform, supply of a signal to the oscillator 11 for control of the generating timing of the RF pulse H 1 , and control of the strength, generating timing, and rotation of the gradient magnetic fields.
  • a display/recording device 18 displays or records the measurement results.
  • the power supply sources 21 and 22 are controlled by the digital arithmetic logic unit 17.
  • the X-axis magneticfield coil assembly of the gradient magnetic field coils 19 consists of two units of coils, i.e., one unit of saddle-shaped coil 19X a and another unit of saddle-shaped coil 19X b , each of which is composed of two coil halves 19X a-1 , 19X a-2 and 19X b-1 , 19X b - 2 respectively.
  • Those units of saddle-shaped coils 19X a and 19X b constitute a pair of X-axis magnetic field coil assembly.
  • Each of coil halves 19X a-1 , 19 Xa-2 , 19Xb-i and 19X b-2 are disposed in such a manner that for instance, the coil half 19X a-1 is faced with the coil half 19X a-2 along the Z-axis.
  • the two units of coils 19X a and 19X b are wound in the opposite directions and are connected to the X-axis part (indicated by the broken line at the left in Fig. 1) of the single power supply source 21. Accordingly, the direction of a magnetic field G x generated by the X-axis coil 19X a at the left of Fig. 2 is opposite to that of a gradient magnetic field G x generated by ther X-axis coil 19X b at the right of Fig. 2. This means that there is a plane at an intermediate point between the coils where the strength of the gradient magnetic field GX is zero (referred to as a "magnetically-zero plane" hereinafter).
  • each unit of saddle-shaped coils 19Y a and 19Y b oppose each other having the Z axis at the center, and extend therealong at positions 90° rotated with respect to the X-axis coil units 19X a and 19X b .
  • a pair of ring-shaped solenoid coils 19Z a and 19Z b oppose each other having the Z axis at the center and extend therealong.
  • a pair of left and right saddle-shaped coils 20X a and 20X b are arranged along the Z axis in such a manner that each overlaps practically a coil half (19X a - 2 and 19X b - 2 ) of each of coil units 19X a and 19X b .
  • a pair of saddle-shaped coils 20Y a and 20Y b are arranged along the Z axis in such a manner that each overlaps practically a coil half (19Y a - z and 19Y b - 2 ) of each of coil units 19Y a and 19Y b , as shown in Fig. 3.
  • a ring-shaped solenoid coil 20Z having the Z axis at its center is arranged in such a manner that it is adjacent to one of the coil units 19Z a and 19Z b .
  • the gradient field G x is shifted parallel to the X axis by an amount ⁇ X.
  • the gradient magnetic field Gy is shifted parallel to the Y axis by an amount ⁇ Y.
  • the gradient magnetic field G z is shifted parallel to the Z axis by an amount ⁇ Z.
  • the combined magnetic field distribution differs from the distribution of the magnetic field G x obtained with the coils 19X a and 19x b alone (i.e., shifted toward the X axis by the amount AX).
  • the solenoid coil 20Z may be alternatively wound concentrically as in the case of the gradient magnetic field coil 19Z b . Any construction may be adopted if the magnetic fields generated by the coils 19Z b and 20Z can be combined.
  • the patient P is placed within the air magnetic field coils 12 while the air magnetic field coils 12 and the stabilizer 13 apply a static magnetic field H o in the Z direction.
  • the selective exciting RF pulse H 1 is generated by the oscillator 11, and the RF pulse H 1 is applied to the patient P in the Y direction through the duplexer 15 and the probe head coil 14, thereby causing nuclear magnetic resonance of a specific atomic nucleus such as hydrogen nucleus in the selected sectional slice plane of the patient P.
  • the gradient magnetic fields G x , Gy,and G z are applied by the gradient magnetic field coils 19 so as to selectively excite the slice plane to which tomographic image is taken (referred simply to as a tomographic image plane).
  • a current is flowed to the solenoid coils 19Z as shown in Fig. 9B in synchronism with the RF pulse H 1 as shown in Fig. 9A so as to apply a gradient magnetic field G z in the Z direction.
  • the slice position or place and thickness are determined by the frequency of the RF pulse H 1 and the gradient angle of the gradient magnetic field G z .
  • the magnetic field generated by the solenoid coil 20Z is not yet applied.
  • the magnetically-zero XY plane at which the gradient magnetic field G z becomes zero is shifted in the positive direction along the Z axis.
  • the slice plane is shifted in the positive direction along the Z axis (to the right in Fig. 8) in correspondence to the shifting magnetic field strength.
  • the slice plane becomes as P 2 and P 3 as shown in Fig. 9. In this manner, the slice plane i.e., tomographic image plane can be moved without requiring mechanical movement of the patient P.
  • the NMR signal is detected by the probe head coil 14 and is supplied to the amplifier 16 through the duplexer 15 for amplification.
  • the amplified NMR signal is A/D converted by the digital arithmetic logic unit 17 so as to rotate G R around the Z axis.
  • image reconstruction is carried out which includes calculation of Fourier transforms on the basis of the NMR signals from the respective rotating direction.
  • the obtained reconstructed image is displayed at the display/ recording device 18 and is recorded as needed.
  • the digital arithmetic logic unit 17 performs control of the generation timing of the RF pulse H 1 , rotating timing and strengths of the gradient magnetic fields, and magnetic field parallel shift timing and strengths of the gradient magnetic field shifting coils 20, through the oscillator 11 and the power supply sources 21 and 22.
  • the gradient magnetic field G z is generated in the Z direction so as to align the selectively generated macroscopic magnetic moment on the Z axis.
  • G s (G x +G z ), that is, a combined gradient field is applied to the patient P, and an NMR signal (FID signal) as shown in Fig. 11E is obtained.
  • NMR signal NMR signal
  • the multi-slice method can be performed utilizing the NMR diagnostic apparatus of the present invention as in the following manner.
  • FID signals in one gradient direction under a predetermined gradient magnetic field are collected for a cross-sectional slice plane P 1 shown in Fig. 8.
  • the exciting current of the solenoid coil 20Z in the same gradient direction is changed so as to shift the slice plane P, to a plane P 2 so as to collect NMR signals.
  • the slice plane is shifted from P 2 to P 3 by means of the solenoid coil 20Z in the same gradient direction and the NMR signals are collected.
  • the coils 19X and 19Y are energized to change the gradient direction of the combined gradient magnetic field G R and NMR signals in this direction are collected.
  • the slice plane is sequentially changed from P 1 to P 2 and from P. 2 to P3 so as to allow collection of NMR signals for each of the slice planes P 2 and P 3 .
  • NMR signals for reconstruction of the image in the slice planes P 2 and P 3 can also be collected.
  • the multi-slice process can be performed within a short period of time.
  • an NMR diagnostic apparatus of the present invention has a simple construction wherein a gradient magnetic field shifting coil as an auxiliary coil and an energizing power supply source therefor are added to a conventional NMR diagnostic apparatus.
  • the slice plane can be shifted freely while maintaining the patient P fixed in position with respect to the magnetic field coils. Slice plane selection can then be performed accurately within a short period of time, reducing imposition on the patient P and improving efficiency in diagnosis.
  • a current flowed to the gradient magnetic field shifting coil is varied, the multi-slice process can be easily performed upon application of each RF pulse H 1 . Diagnosis time can be significantly reduced, again reducing imposition on the patient.
  • an RF pulse is a 90° selective exciting pulse.
  • echo signals can be collected as NMR signals using a 90°-180° pulse or NMR signals compensated by a relaxation time T i using a 90°-180° pulse can be collected.
  • a magnet device for generating a static magnetic field may be a conductive air magnet, a super-conducting air magnet, a conductive electromagnet or a permanent magnet.
  • the units of coils 19X a and 19X b and the units of coils 19Y a and 19Y b of the gradient magnetic coils 19 are wound in the opposite directions.
  • these coils may be wound in the same direction, and connections may be performed in such a manner that energizing currents are flowed in the opposite directions.
  • the multi-slice method described above can be modified by the following method. After collecting FID signals at a first gradient angle in a first slice plane P 1 , FID signals are collected at a second gradient angle in a second slice plane P 2 . Then, FID signals are collected at a third gradient angle in a third slice plane P 3 . The slice plane is returned to the first slice plane P 1 to collect FID signals. Thereafter, FID signals are collected at a different gradient angle every time the gradient angle is changed. In this manner, a series of FID signals can be collected.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Claims (5)

1. Vorrichtung (100) zum Untersuchen eines Objektes (P) durch Kernmagnetresonanz, mit:
einer Magneteinrichtung (12; 13) zum Anlegen eines statischen Magnetfeldes (Ho) an das Objekt (P) entlang einer Längsachse hiervon;
einer ersten Spuleneinrichtung (19), die entlang der Längsachse angeordnet und selektiv erregbar ist, um an das Objekt (P) ein erstes Gradientmagnetfeld (Gx; Gy; Gz) anzulegen, das zusammen mit dem statischen Magnet feld (H0) ein vorbestimmtes Magnetfeld in einer Scheibe (P1; P2; P3) des Objetes (P) ergibt, und auch zum Anlegen eines zweiten Gradientmagnetfeldes (GR; Gs) an die Scheibe (P1; P2; P3) des Objektes (P), um einen Projektionswinkel von Kernmagnetresonanzsignalen zu definieren;
einer Sondenkopfspuleneinrichtung (14) zum Anlegen von Hochfrequenzimpulsen (H1) an die Scheibe (P1; P2; P3) des Objektes (P), um einen Kern darin anzuregen, an dem gerade das durch das statische Magnetfeld (Ho) und das erste Gradientmagnetfeld (Gx; Gy; Gz) überlagerte vorbestimmte Magnetfeld liegt, und zum Erfassen von von der Scheibe (P1; P2; P3) des Objektes (P) abgeleiteten Kernmagnetresonanzsignalen; und
einer Rekonstruktionseinrichtung (16), die die von der Scheibe (P1; P2; P3 des Objektes (P) erhaltenen Kernmagnetresonanzsignale durch die Sondenkopfspuleneinrichtung (14) bezüglich einer Vielzahl der Projektionswinkel des ersten Gradientmagnetfeldes (Gx; Gy; Gz) empfängt und eine Vielzahl von Computertomographiebildern für die Kerndichte der Scheibe (P1; P2; P3) des objektes (P) aufgrund der Kernmagnet resonanzsignale rekonstruiert,
dadurch gekennzeichnet, daß
eine zweite Spuleneinrichtung (20) entlang der Längachse angeordnet und selektiv erregbar ist, um an die Scheibe (P1; P2; P3) des Objektes (P) ein Schiebemagnetfeld anzulegen, das dem ersten Gradientmagnetfeld (Gx; Gy; Gz) überlagert ist, um eine magnetische Nullebene des ersten Gradientmagnetfeldes (Gx; Gy; Gz) in einer Richtung zu verschieben, die senkrecht zur magnetischen Nullebene ist.
2. Vorrichtung (100) zum Untersuchen eines Objektes (P) durch Kernmagnetresonanz nach Anspruch 1, dadurch gekennzeichnet, daß
die erste Spuleneinrichtung (19) aufweist:
eine erste Gradientmagnetfeldspule (19X), die entlang der Längsachse des Objektes (P) angeordnet ist und deren Feldstärke sich linear in entgegengesetzter Weise entlang einer ersten Achse (X) senkrecht zur Längsachse des Objektes (P) ändert;
eine zweite Gradientmagnetfeldspule (19Y), die entlang der Längsachse des Objektes (P) angeordnet ist und deren Feldstärke sich linear in einer entgegengesetzten Weise entlang einer zweiten Achse (Y) senkrecht aur Längsachse sowie zur ersten Achse (X) ändert und
eine dritte Gradientmagnetfeldspule (19Z), die entlang der Längsachse des Objektes (P) angeordnet ist und deren Feldstärke sich linear in einer entgegengesetzten Weise entlang einer dritten Achse (Z) parallel zur Längsachse des Objektes (P) ändert.
3. Vorrichtung (100) zum Untersuchen eine Objektes (P) durch Kernmagnetresonanz nach Anspruch 2, dadurch gekennzeichnet, daß
die erste Gradientmagnetfeldspule (19X) zwei Einheiten von Elektromagnetspulen als einer Paarkombination (19Xa; 19Xb) aufweist, wobei jede Einheit hiervon aus zwei sattelförmigen Spulenhälften als einer Paarkombination (19Xa-1; 19Xa-2; 19Xb-1; 19Xb-2) gebildet ist, die symmetrisch in Längsrichtung un die dritte Achse (Z) angeordnet und unter einem gegenbenen Abstand getrennt sind,
die zweite Gradientmagnetfeldspule (19Y) zwei Einheiten von Elektromagnetspulen als eine Paarkombination (19Ya; 19Yb) aufweist, wobei jede Einheit hiervon aus zwei sattelförmigen Spulenhälften als einer Paarkombination (19Ya-1; 19Ya-2; 19Yb-1; 19Yb-2) besteht, die symmetrisch in Längsrichtung um die dritte Achse (Z) sowie senkrecht zur ersten Gradientmagnetfeldspule (19X) angeordnet sind, und
die dritte Gradientmagnetfeld spule (19Z) ein Paar von elektromagnetspulen aufweist, wobei das Paar durch zwei Solenoid-Spulenhälften (19Za; 19Zb) gebildet ist, die symmetrisch in Längsrichtung um die dritte Achse (Z) vorgesehen sind, und
die zweite Spuleneinrichtung (20) aufweist:
eine erste Schiebemagnetfeldspule (20X), die aus zwei sattelförmigen Elektromagnetspulenhälften (20Xa; 20Xb) besteht, wobei jede Spulenhälfte neben einer der jeweiligen sattelförmigen Spulenhälften (19Xa-1; 19Xa-2; 19Xb-1; 19Xb-2) der ersten Gradientmagnetifeldspule (19X) liegt;
eine zweite Schiebemagnetfeldspule (20Y), die aus zweit sattelförigen Elektromagnetspulenhälften (20Ya; 20Yb) besteht, wobei jede Spulenhälfte neben einer der jeweiligen sattelförmigen Spulenhälften (19Ya-1; 19Ya-2; 19Yb-1; 19Yb-2) der zweiten Gradientmagnetfeldspule (19Y) liegt, und
eine dritte Schiebemagnetifeldspule (20Z), die aus einer Solenoidspule besteht, welche neben einer der Solenoid-Spulenhälften (19Za; 19Zb) der dritten Gradientmagnetfeldspule (19Z) liegt.
4. Vorrichtung (100) zum Untersuchen eines Objektes (P) durch Kernmagnetresonanz nach Anspruch 1, dadurch gekennzeichnet, daß
-die Scheibe des Objektes (P) für die Computertomographiebilder ein Querschnittsscheibe (Pi; P2; P3) des Objektes (P) bezüglich der Längsachse ist.
5. Vorrichtung (100) zum Untersuchen eines Objektes (P) durch Kermagnetresonanz nach Anspruch 1, dadurch gekennzeichnet, daß
die Scheibe des Objektes (P) für die Computertomographiebilder eine Sagittal-Scheibe (P1; P2; P3) des Objektes (P) bezüglich der Längsachse ist.
EP83111154A 1982-11-08 1983-11-08 NMR-Diagnosevorrichtung Expired EP0108421B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP196483/82 1982-11-08
JP57196483A JPS5985651A (ja) 1982-11-08 1982-11-08 診断用核磁気共鳴装置

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EP0108421A2 EP0108421A2 (de) 1984-05-16
EP0108421A3 EP0108421A3 (en) 1985-07-31
EP0108421B1 true EP0108421B1 (de) 1989-02-22

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US4656423A (en) 1987-04-07
EP0108421A3 (en) 1985-07-31
JPS5985651A (ja) 1984-05-17
JPH0243493B2 (de) 1990-09-28
DE3379239D1 (en) 1989-03-30
EP0108421A2 (de) 1984-05-16

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